1. Field of the Invention
The invention concerns a voltage-limiting circuit device for a battery charger, and more particularly a voltage-limiting circuit device that permits linear adjustments so that the device is compatible with any battery set regardless of the saturation voltage VS.
2. Description of the Prior Art
In the instance (1) where charging is carried out with respect to the output terminals of a multiple voltage output circuit that exhibits a forward diode voltage drop effect such as is disclosed in U.S. Pat. No. 5,118,993 granted to the Applicant hereof, by connecting a battery pack directly in parallel thereto, or (2) where, per traditional practice, a diode is connected directly in parallel with the battery pack to provide voltage-limiting tributary currents by the realization of a diode-forward voltage drop VF, the battery pack terminal voltage VB will increase gradually in proportion to accumulated charging, as the battery pack is being charged, to a level close to the forward diode voltage drop VF. When the forward diode voltage drop matches the battery pack terminal voltage VB that is increasing commensurate with cumulative charging, a steady state is reached. In that event, however, should the voltage drop in the forward direction because the parallel diode voltage drop VF differs from the rated saturation voltage VS of the battery pack, since the diode forward voltage drop VF is subject to a stage by stage fluctuation at an approximate rate of 0.7V per series connection of diode, it would be very difficult to effect matching with the rated battery pack saturation voltage by altering serial connection of diodes. Indeed, up to this date there has been no revelation or disclosure available which teaches linear adjustment or matching between both, so it follows that the traditional practice of connecting diodes directly in parallel with the battery pack will inevitably incur two shortcomings in the course of charging: (1) where the diode is not protected by a current limiter connected in series therewith, then the current flowing through the diode when both the diode forward voltage drop VF and the battery pack terminal voltage VB reach a steady state will increase abruptly, eventually resulting in burning of the diode; and (2) the diode forward voltage drop VF will be inconsistent with the charging voltage nominally required by the battery pack, resulting inevitably in retarded or inadequate charging if the voltage drop VF is the less than the required charging voltage, or alternatively overcharging if the voltage drop VF is greater than the required charging voltage.